A device is known, which is capable of detecting a vehicle running ahead of an own vehicle or detecting a distance between a preceding vehicle and the own vehicle through a camera mounted on the own vehicle (cf., for instance, Patent Reference 1). As the camera used in this device operates mainly during running of the vehicle, contaminants tend to adhere to a front surface of the lens. If the lens is badly contaminated, it becomes impossible to accurately detect a photographic object such as a preceding vehicle. Accordingly, it is desired to include a means to detect contaminants that adhere to an on-vehicle camera and gives a warning for cleaning the lens to the driver or automatically washes it.
In order to solve this problem, a method of detecting contaminants adhering to the camera has been conceived (cf., for instance, Patent Reference 2). In this method of detecting contaminants, adhered contaminants are detected by capturing images at a plurality of moments by a single camera and extracting differences between the images. According to this method, it is possible to detect contaminants and automatically wash them.